The project is designed to elucidate the role of xenobiotic-metabolizing enzymes in skin as mediators of toxicity of environmental agents. Mixed-function oxidase (including aryl hydrocarbon hydroxylase), glutathione S-epoxide transferase, UDP-glucuronyl transferase, and L-histidase activities are measured in pieces of whole skin or epidermis, or in microsomes or cytosol from skin of hairless mice (Hrs/J) after exposure of the mice to ultraviolet radiation, polycyclic hydrocarbons, chlorinated hydrocarbons, etc. The wavelength of maximum absorbance in the carbon monoxide spectra of reduced cytochrome P-450 is identified after separating the cytochrome from contaminating mitochondrial pigments.